Prestressed roller bearings are known. See Italian Pat. No. 418,088, issued to Steffenini, Feb. 5, 1947, and U.S. Pat. No. 3,765,071, issued to Bowen, Oct. 16, 1973. These bearings are used to support a rotating shaft upon or within a non-rotating member, in a frictionless manner.
Common problems with conventional prestressed roller bearings are: (1) finding a method of assembly and prestressing that does not damage the rollers and races, some of which parts have polished high precision surfaces, and (2) special talent or training is required on the part of the installation mechanic in the field that installs such bearings on the supported shaft.
Prestressed roller bearings are commonly assembled by placing the rollers inside the outer race, and then using extreme force to press the inner race within the rollers. This force fit of the inner race prestresses the rollers but also causes an axial sliding of the surfaces of the inner race across the surfaces of the rollers. This is destructive to the rollers and races at the point of contact. This yields a bearing that has been weakened in an unknown and individually varying, non-standard manner. To a certain extent, this destruction can be mitigated by rotating the inner race as it is pressed between the rollers. However, this is a difficult and unpredictable technique and also causes scarring of the surfaces. See U.S. Pat. No. 2,594,578, issued to McNicholl, Apr. 29, 1952.
An alternative method of assembly of prestressed roller bearings is to first assemble the bearing in an unprestressed manner. The bearing is then installed on the supported shaft by pressing it on a tapered end portion of the shaft. By forcing the bearing down over the tapered shaft, the expanding diameter of the tapered shaft stretches the diameter and circumference of the inner race to the point that it prestresses the rollers. The problem with this method is that it requires a special tapered shaft and special training and skill on the part of the individual who installs the bearing on the shaft. If the bearing is pressed too far on the shaft then the rollers are overly prestressed. If the bearing is not pressed farther enough down the shaft then the rollers are not adequately prestressed. The adequacy of the prestressing cannot be quality controlled in the factory setting, since the prestressing does not take place until the installation on the supported shaft in the field.
An effort has been made to facilitate this method of prestressing-by-installation on the shaft. See U.S. Pat. No. 4,893,948, issued to Hoch, Jan. 16, 1990. In Hoch, an assembled and as yet unprestressed bearing with an inner race with a conical bore is mounted without prestressing on a bearing seat on the supported shaft. The bearing seat is attached to the supported shaft and has a conical clamping sleeve. After installation, the clamping sleeve on the shaft is forced a calibrated distance into the inner race of the bearing, between the supported shaft and the inner race of the bearing. In this manner, the inner race of the bearing is stretched, thereby prestressing the rollers. This is a method of prestressing the rollers during or after installation upon the shaft. Again, this method requires special training on the part of the installing individual, and takes place at the point of installation, outside of the manufacturing facility for the bearing and outside of the quality control of such facility.
An alternative approach of prestressing upon installation is found in U.S. Pat. No. 4,708,498, issued to Labedan and Merle, Nov. 24, 1987. Here the bearing is manufactured in two halves that are unprestressed. At the time of installation, the two halves are assembled on the supported shaft by compression within the cavity of a outer mount that is installed around the two halves. Again this provides for prestressing upon installation on the shaft, outside of the manufacturing facility. It requires special training on the part of the installer and is beyond the quality control of the factory. Furthermore, only certain bearing situations permit this half-and-half sort of bearing, and the design limits performance of the bearing after installation.
It is an object of the present invention to provide a prestressed roller bearing that is manufactured and prestressed within its manufacturing facility, and within the quality control of that facility.
It is a further object of the present invention to manufacturer such prestressed roller bearing and assemble it in a manner that does not provide for pressured axial sliding of the surfaces of the rollers over the surfaces of the races, so as to scar and damage the parts.
It is a further object of the invention to provide for a prestressed roller bearing that can be installed on a normal supported shaft by the normal methods of installing an unprestressed roller bearing, without special training or skill on any other part of the installing individual.